Glial cells have a profound influence on neuronal functions. Oligodendrocytes and Schwann cells ensheath axons with myelin to enable rapid nerve impulse conduction. Astrocytes support neurons in multiple ways, and also influence synaptic development and function. A variety of signals are transmitted between neurons and glia. The transmission and reciprocal exchange of these signals are based on the contact or close apposition of neuronal and glial cell elements. Thus one of the key questions in the field of neuron-glia interactions is how these intricate spatial arrangements are established during development and how they are maintained in the adult nervous system. This Program Project aims to understand the role of three groups of molecules, namely heparan sulfate proteoglycans, the NG2 chondroitin sulfate proteoglycan, and ephrin-A/EphA cell contact-dependent signaling molecules, in the establishment and maintenance of neuronglia communication. These three groups of molecules have a strong involvement in the development and differentiation of glial cell types. Our preliminary data further implicate them in various types of neuron-glia interactions. Components I and II investigate the role of glial proteoglycans, heparan sulfate proteoglycans and the NG2 chondroitin sulfate proteoglycan, respectively, on Schwann cell and oligodendrocyte development and myelination. Component III focuses on the role of ephrin/Eph proteins in the cell surface interactions between dendritic spines and perisynaptic astrocytes to elucidate molecular mechanisms of neuron-glia crosstalk at synapses. While the three Components investigate different families of molecules in different cellular systems, they share the same basic research strategy, combining in vivo analysis of mutant mice with in vitro analysis of primary cell cultures derived from mutant mice. This strategy will allow direct comparison of the in vivo consequences of ablating a given molecule and the behavior of mutant cells in vitro for each of the three molecular groups. Extensive collaborations within the Program will produce synergistic achievements more widely applicable to neuron-glia interactions in general. Furthermore, the Program will explore new lines of research at the interfaces between Components, and obtain answers to important questions beyond the immediate reaches of each component. This Program Project will impact the understanding of molecular and cellular crosstalk by which neurons and glial cells establish and maintain neuron-glia communication, providing molecular insight into demyelinating diseases and neurological disorders in which the disruption of neuron-glia communication is an initiating factor.